Why do people get so mad at you for this?

Why do people get so annoyed and mad with you when you make mistakes? No one is perfect...so why such annoyance? Like I was hanging out with my sisters and I accidentally pushed and dropped my younger sister's make-up bag..none of the makeup broke...and yes all of it fell on the floor but I was trying to pick it up but she got all angry and pushed me aside to pick it up herself. And then both my sisters were fuming at me, I decided to just ignore it but what gives? I didn't do it on purpose and I'm not perfect and I can be clumsy sometimes...so why all the anger? O.O